Manifold porting

[Erik the Awful]

this could all be an exercise in futility at best

I wouldn't call it an exercise in futility. Removing the casting flash in the runners is a good idea. Removing the casting flash in the middle of the plenum is just practice and won't kill power.

Only downstream of the injectors...

Not above the injectors it won't!

Everything's a TBI in my mind, and I forget that MPFI exists. Your statements are fairly true, but why do the extra work? Leaving the surface at 120 grit isn't killing power.